This invention relates to plastic pipe forming apparatus, and more particularly to a mandrel for forming a belled socket in the end of a pipe, the socket being formed with an annular seal pocket.
A common method for joining pipe sections end to end is to provide on one end of each pipe section a socket sized to receive the straight end of the adjoining pipe section. To provide a fluid-tight fit, it also is common practice to locate a seal member between the two pipe sections.
This is done by providing an annular space or pocket within the belled, or socket, end into which a seal member may be placed. The seal member is located in such a manner that upon inserting the adjoining pipe section the seal member abuts both pipe sections and thus is secured in place.
In this manner it is also possible to allow a degree of freedom in the fit of the sections, so that the alignment of the joint need not be exact. Also the pipeline may expand or contract, without affecting the effectiveness of the seal.
The use of this type of joint is particularly common in plastic pipelines. Accordingly, a number of devices of the same general classification as that of the presently disclosed device have been employed to produce belled sockets on the end of plastic pipe sections.
Some of the prior art devices mold the exterior of the socket. Since the pipe wall is of a predetermined thickness, such a socket is formed on the inside of the pipe. However, this type of apparatus cannot be relied upon to produce a product of close tolerances because of differences in wall thickness and other factors. Accordingly, with this type of manufacture, the joints are prone to leak. Moreover, a separate mold is required for each different pipe wall thickness since the interior size of the socket must remain the same.
Other prior art devices have internal molding mandrels. The problem encountered with an internal molding mandrel is one of forming the annular seal pocket in the socket. The molding apparatus includes an annular ring, the seal-pocket-molding parts of which must be retracted into the mandrel before it can be withdrawn from the pipe; else the lip of the pipe will be destroyed upon separation of the pipe from the mandrel.
The apparatus for extending and retracting the segments of the mandrel forming the annular ring in the prior art devices is complex and malfunction-prone. Some such devices include pivoted segments which must be extended in a specified order. Others have segments which are collapsible upon rotation.
Accordingly, it is the general object of the present invention to provide a belling mandrel for enlarging and forming a belled socket on the end of a plastic pipe.
Another object is to provide a belling mandrel of simple construction, having moving parts which function repeatedly without malfunction.
A further object is to provide component parts which have very large bearing surface areas.
Yet another object is to provide a belling mandrel frame and drive assembly which is simple and rugged in construction.
A still further object is to provide a belling mandrel which is accurate, simple, rugged and the design for which may be scaled up or down for use in a wide range of pipe sizes.
These and other objects and advantages of the present invention, and the manner in which they are achieved will be made apparent in the following specification and claims.